1. Field of Invention
This invention relates generally to a liquid ink printing apparatus, and more particularly to a liquid ink printing apparatus having a cross flow air system for drying a recording medium and ink deposited on the recording medium.
2. Description of Related Art
Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based or thermal printer, have at least one printhead from which droplets of ink are directed towards a recording medium. Within the printhead, the ink is contained in at least one channel, or preferably in a plurality of channels. Power pulses cause the droplets of ink to be expelled as required from orifices or nozzles at the end of the channels.
In a thermal ink-jet printer, the power pulse is usually produced by a heater transducer or a resistor, typically associated with one of the channels. Each resistor is individually addressable to heat and vaporize ink in one of the plurality of channels. As voltage is applied across a selected resistor, a vapor bubble grows in the associated channel and initially bulges from the channel orifice, followed by collapse of the bubble. The ink within the channel then retracts and separates from the bulging ink, to form a droplet moving in a direction away from the channel orifice and towards the recording medium. When the ink droplet hits the recording medium, a drop or spot of ink is deposited. The channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink.
The ink jet printhead may be incorporated into either a carriage type printer, a partial-width-array type printer, or a page-width type printer. The carriage type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge. The combined printhead and cartridge assembly is attached to a carriage, which is reciprocated to print one swath of information (having a width equal to the length of a column of nozzles) at a time on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion of the swath, so that the next printed swath is contiguous or overlapping with the previously printed swath. This procedure is repeated until the entire page is printed. In contrast, the page-width printer includes a stationary printhead having a length sufficient to print across the width or length of a sheet of recording medium at a time. The recording medium is continually moved past the page width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page width ink-jet printer is described, for instance, in U.S. Pat. No. 5,192,959.
Many liquid inks, and particularly those used in thermal ink jet printing, include a colorant or dye and a liquid, which is typically an aqueous liquid vehicle, such as water, and/or a low vapor pressure solvent. The ink is deposited on the substrate to form an image in the form of text and/or graphics. Once deposited, the liquid component is removed from the ink and the paper to fix the colorant to the substrate by either natural air drying or by active drying. In natural air drying, the liquid component of the ink deposited on the substrate is allowed to evaporate and to penetrate into the substrate naturally without mechanical assistance. In active drying, the recording medium is exposed to heat energy of various types, which can include infrared heating, conductive heating and heating by microwave energy.
Active drying of the image can occur either during the imaging process or after the image has been made on the recording medium. In addition, the recording medium can be preheated before an image has been made to precondition the recording medium in preparation for the deposition of ink. Preconditioning the recording medium typically prepares the recording medium for receiving ink by driving out excess moisture, which can be present in a recording medium such as paper. Not only does this preconditioning step reduce the amount of time necessary to dry the ink once it is deposited on the recording medium, but this preconditioning step also improves image quality by reducing paper cockle and curl, which can result from too much moisture remaining in the recording medium.
Various drying mechanisms for drying images deposited on recording mediums are illustrated and described in the following disclosures, which may be relevant to certain aspects of this invention.
U.S. Pat. No. 4,970,528 to Beaufort et al., describes a method for uniformly drying ink on paper from an ink jet printer. The printer includes a uniform heat flux dryer system including a 180xc2x0 contoured paper transport path for transferring paper from an input supply tray to an output tray. During transport, the paper receives a uniform heat flux from an infrared bulb located at the axis of symmetry of the paper transport path. Reflectors are positioned on each side of the infrared bulb to maximize heat transmission from the bulb to the paper during the ink drying process.
U.S. Pat. No. 5,029,311 to Brandkarnp et al., describes a fluorescent lamp utilized in a document scanning system that is environmentally and thermally stabilized by means of a bifurcated heater control assembly. A heater blanket is wrapped around the entire surface of the lamp, including the end areas surrounding the filaments but exclusive of the aperture through which light is emitted.
U.S. Pat. No. 5,274,400 to Johnson et al. describes an ink path geometry for high temperature operation of ink jet printheads. A heating means is positioned close to a print zone for drying of the print medium. The heating means includes a print heater and a reflector, which serve to concentrate the heat on the bottom of the print medium through a screen.
U.S. Pat. No. 5,287,123 to Medin et al. describes a color ink jet printer having a heating blower system for evaporating ink carriers from the print medium after ink-jet printing. A print heater halogen quartz bulb heats the underside of the medium via radiant and convective heat transfer through an opening pattern formed in a print zone heater screen.
U.S. Pat. No. 4,982,207, to Tunmore et al. describes a heater construction for an ink jet printer having a rotary print platen for holding and transporting a print sheet through a print path. The platen heater includes a hollow shell having vacuum holes for sheet attachment. A heating foil is detachably mounted in a heat transfer relation with the interior periphery of the shell.
U.S. Pat. No. 5,005,025, to Miyakawa et al. describes an inkjet recording apparatus for recording, which fixes ink through evaporation of an ink solvent. The apparatus includes a heating member extending both upstream and downstream with respect to a recording area and a conveying direction of the recording sheet. The heating member contacts the recording sheet to assist in fixing the ink.
U.S. Pat. No. 5,406,321, to Schwiebert et al. describes an ink jet printer and a paper preconditioning preheater for the ink jet printer. The paper preconditioning preheater has a curved surface and a multi-purpose paper path component to accomplish direction reversal for the paper. The paper contacts the preheater, which dries and shrinks the paper to condition it for a printing operation. The preheater is a thin flexible film carrying heater elements that is suspended in air to provide extremely low thermal mass and eliminate the need for long warm up times.
Despite these various designs, a need exists for an ink jet printer dryer system that efficiently works to dry printed substrates. This need is particularly evident in the field of color ink jet printing, where one color printed area must be dried, either partially or completely, prior to printing with a second color. Such a system is required in order to prevent inter-color bleed, a problem that results when a subsequently printed color bleeds into a previously printed color, or vice-versa, causing a print image defect. That is, when two colors are printed in sequence, either on top of or adjacent to one another, the colors will unintentionally mix with each other if there is insufficient drying of the first printed color prior to printing the second color. This creates a gross deficiency in the print quality, affecting the sharpness of the edges and the overall resolution of the image.
Furthermore, the need exists in the field for improved active drying systems for ink jet printing applications. As the print speed, color range and ink coverage of ink jet printers increases, the need for active drying mechanisms in the printers also increases. An aspect of such active drying systems is airflow through the printer, and particularly through the recording medium path (i.e, the transport path and the print zone). Airflow is important because it serves at least two functions in the printer. First, airflow assists in the evaporation of the liquid carrier from the printed ink to dry the printed image, permitting faster handling of the printed materials. Second, airflow can provide a cooling effect to the printhead, which tends to reduce thermally driven density variations in the ink resulting from printhead temperature changes. Furthermore, positive airflow through the printer has the additional effect of removing effluents, by-products produced during rapid drying of the liquid inks. These by-products otherwise tend to condense on cooler surfaces, which could lead to contamination on the recording medium, paper handling difficulties, or end-user disapproval.
Furthermore, a need exists for printer dryer designs that will efficiently and quickly dry the printed image without causing image or paper defects. Such printer dryer designs will permit still higher increases in paper throughput speed, permitting higher speed printing.
This invention provides an active drying system incorporating a cross flow air system that realizes improved drying of the printed recording medium and of the printer components.
This invention especially provides an active drying apparatus having a cross flow air system that can be incorporated into a printing apparatus, such as an ink jet printer.
The cross flow air system of this invention provides higher printing efficiency, higher print quality, and lower cost.